Double loop antenna



May 18, 1965 M. G. CHATELAIN I DOUBLE LOOP ANTENNA Filed May 15, 1961 INVENTOR. MAURICE GEOR GE CHATELAIN United States Patent 3,184,746 DOUBLE L061 ANTENNA Maurice George Chatelain, San Diego, Calif., assignor to The Ryan Aeronautical (10., San Diego, Calit. Filed May 15, 1961, Ser. No. 150,108 Claims. (Cl. 343-742) This invention relates to antennas, and more particularly to a novel type of loop antenna.

Background In airborne devices, antennas should be light-weight, small, and compact. Furthermore, since the antennas are usually positioned remote from their associated operating equipment, connecting cable must be used to connect the antennas to the equipment. The antennas should therefore have an inherent characteristic impedance that matches the characteristic impedance of the connecting cables, without the need for intermediate impedancematching elements. This condition is desirable for optimum lightweight transfer of energy between the antenna and the cable.

In many cases of airborne navigational systems, such as direction-finding and instrument-landing for example, it is generally recognized that the most satisfactory antennas are the half-wave loop type. Unfortunately, however, these antennas have a low characteristic impedance, which poses problems in connecting them to the widelyused 50-ohm coaxial connecting cables.

Furthermore, a rectangular loop-antenna radiates and/ or receives in the direction opposite that in which the energy feeds. This means that a corner-fed antenna requires unusual mounting, and for axial radiation an axial feed is required.

On the other hand, a center-fed loop antenna, which has certain advanttages, requires a different space configuration than a rectangular loop-antenna.

Objects and drawings It is therefore the principal object of my invention to provide an improved antenna.

It is another object of my invention to provide an antenna that is lightweight and compact.

It is a further object of my invention to provide an antenna whose characteristic impedance is such as to match that of the connecting cable.

It is still another object of my invention to provide an improved antenna that is easily fed, and provides a symmetrical and sharply directional pattern.

The attainment of these objects and others will be realized from the following specification, taken in conjunction with the drawings, in which:

FIGURE 1 is a pictorial representation of my double loop antenna;

FIGURE 2 shows the equivalent electrical circuit of my double loop antenna;

FIGURE 3 shows, symbolically, the radiation pattern of my invention;

FIGURE 4 shows how my double loop antenna is associated with horizontally polarized radiation; and

FIGURE 5 shows how my double loop antenna is associated with vertically polarized radiation;

Brief description of the invention Broadly speaking, my invention contemplates a double loop antenna comprising two parallel, spaced-apart loops. In accordance with my invention, the dimensions,

3,184,746 Patented May 15, 1965 ice spacing, shape, and other parameters of the loops determine the antennas characteristic impedance, electrical characteristics, and radiation pattern.

Detailed description of the invention It will be seen from the pictorial representation of FIGURE 1, that my double loop antenna 10 comprises two parallel spaced-apart U-shaped members 12 and 14, which may be made of metal rods or tubing. The two proximal adjacent ends 16 and 18 of members 12 and 14 are mounted in the end receiving sockets 19 and 21 of a first insulating mounting block 20, while the distal adjacent ends 22 and 24 of members 12 and 14 are mounted in the end receiving sockets 23 and 25 of a second insulating mounting block 26. Mounting blocks 20 and 26 are fastened to an electrically conductive ground plate 28.

It will be seen from the cross sectional view of mounting blocks 20 and 26 that the proximal end 16 of U-shaped member 12, is connected by a connecting wire 34 to the central twire 38 of a coaxial connecting cable 42. Similarly, the distal end 24 of U-shaped member 14 is connected by connecting wire 36 to the outer conductor 40 of coaxial connecting cable 42.

The proximal end 18 of U-shaped member 14 and the distal end 22 of U-shaped member are positioned in their respective mounting blocks 20 and 26 above ground plate 28.

It will be realized that each U-shaped member 12 and 14 coacts with ground plate 28 to eifectively produce a rectangular loop, whose effective length may be equal to one-half of the wavelength used, in order to provide optimum antenna characteristics.

Operation 0 the invention To understand the operation of my invention, assume that the antenna 10 is being used to transmit energy from an undisclosed source. The energy travels from the source along central wire 38 of the coaxial connecting cable 42, up connecting wire 34 to proximal end 16 of U-sh-aped member 12, and along member 12. The distal end of member 12 is spaced from, and therefore capacitively coupled to, ground plane 28, and the energy traverses this capacitive coupling. This arrangement effectively produces a first rectangular loop that is being fed from the proximal end thereof.

A similar analysis will show that energy also travels from the source along the outer conductor 4% of the connecting cable 42., through connecting wire 36 to the distal end 24 of U-shaped member 14, along member 14 to its proximal end 13, and thence through the capacitive coupling between end 18 and ground plate 28. This arrangement effectively provides a second loop that is fed from the distal end thereof.

It will be noted that the loops have a parallel, spacedapart relation, and that energy must pass from one loop to the other by means of the inductive and capacitive coupling between them. The inductive coupling is procured by the magnetic fields produced by energy flowing along the. parallel members 12 and 14, while the capacitive coupling results from the spaced-apart relation of members 12 and 14.

Equivalent electrical circuit Referring now to FIGURE 2, there is shown the equivalent electrical circuit for my double loop antenna. Inductances 44 and 46 represent the, inductive reactance 3 produced by energy flowing along the U-shaped members 12 and 14. Capacitance 48 represents the capacitive coupling between the spaced-apart U-shaped members 12 and 14, and the capacitance between ends 18 and 22 and ground plane 28. Capacitances t? and 52 represent the capacitance between ground plane 28, and the straight portions of members 12 and 14.

It was previously pointed out that an antenna should have an impedance that matches that of the connecting cabtle. In my invention, the antennas characteristic impedance is determined by the length of the members 12 and 14, by the spacing between them, and by their distance above the ground plate.

It should also be noted that the center frequency of the antenna is also determined by these parameters.

A balance between frequency and impedance is obtained by suitable selection of these values.

As previously discussed, a rectangular loop antenna radiates from the corner opposite its feed point. FIG- URE 3 shows the radiation pattern of my double loop antenna in a symbolic manner. Loop 54 is fed at its lower-left corner 56, and radiates from its upper right corner 58, as shown by arrow 66. Loop 62 is fed at its lower right corner 64, and radiates from its upper left corner, as shown by arrow 68. The separate radiation patterns indicated by arrows 6t and 68 produce an overall radiation pattern whose direction is indicated by arrow 70. The pattern is a symmetrical, highly directional beam of any desired frequency. Thus, my double .loop' antenna has the desired radiation pattern and characteristic impedance.

One more characteristic of my antenna should be mentioned. The polarization of the. transmitted beam is parallel to the plane of the loop. As symbolically shown in FIGURE 4, when the loops l2 and 14 are horizontal, the resultant beam 72 is horizontally polarized.

FIGURE 5 shows in a similar manner, that when loops 12 and 14 are vertically oriented, the resultant beam 74 is vertically polarized.

Even though the foregoing explanation has been offered in terms of a transmitting antenna, my double loop antenna may be readily used for either transmitting or receiving energy. When used as a receiving antenna, the reception pattern is the same as the previously explained transmission pattern.

My novel antenna may be used in many applications. One particularly good use for my double loop antenna is as part of the landing system of an airplane. In the usage, my antenna is mounted on the front .of the airplane, and picks up the radiations that define the glide path that leads the airplane down to the airport, the received radiations being used in the well known manner.

Advantages In summary it will be realized that my novel double loop antenna has many advantages over prior-art devices. First, it is lightweight and compact. Second, it provides a symmetrical, highly directional pattern. Third, it may be designed for any desired frequency. Fourth, it may have an inherent characteristic impedance that matches the characteristic impedance of connecting cable without the need for any impedance-matching elements. Fifth, my double loop antenna is extremely rugged and easy to mount. Finally, my antenna may be readily used with either horizontally or vertically polarized radaitions.

It is understood that minor variation from the form of the invention disclosed herein may be made without departure from the spirit and scope of the invention, and that the specification and drawing are to be considered as merely illustrative rather than limiting.

I claim:

1. An antenna comprising:

a first rectangular loop;

a second rectangular loop positioned parallel to but spaced apart from said first loop, whereby energy flows from one said loop to the other said loop through the inductive and capacitive coupling between saidloops; means fo-rfeeding one said iloop at one corner thereof;

means for feeding said other loop at another corner thereof, said feeding means and the dimensions and spacing of said loops producing a unidirectional radiation pattern.

2. An antenna comprising:

a first loop, said loop comprising acne-quarter wave U--shaped member having a first and a second end;

a second loop comprising a one-quarter wave U-shaped member having a first and a second end;

means for positioning said loops parallel but spacedapart from each other with the first end of each loop adjacent the second end of said other loop;

a first feed 'wire connected to said first end of said first loop; and V a second feed wire connected to said first end of said second loop, whereby energy flows between said loop-s through the inductive and capacitive coupling therebetween.

3. An antenna compnising:

a first loop, said loop comprising a one-quarter wave U-shaped member having a first and a second end;

"a second loop comprising a one-quarter wave U-shaped member having a first and a second end;

means for positioning said loops par-allel but spacedapart from each other with the first end of each loop adjacent the second end of said other loop, said positioning means comprising mounting blocks having end-receiving sockets therein;

a first feed wire connected to sm'd first end of said first loop; and v a second feed wire connected to said first end of said second loop, whereby energy flows between said loops through the inductive and capacitive coupling therebetween. V a

4. A double loop antenna comprising:

a first one-quarter wave U-sha-ped member having a first end and a second end;

a second one-quarter wave U-shaped member having a first end and a second end;

an electrically conductive plate;

means for positioning said first and second members parallel but spaced apart from each other, and perpendicular to said plate, said positioning means comprising insulating mounting blocks having two end-receiving sockets therein, each block having the first end of one member and the second end of said other member positioned in sockets thereof;

a first feed wire connected to said first end of said first member; 7 a

and a second feed wire connected to said first end of said second member.

5. A double loop antenna comprising:

a first one-quarter wave U-shaped member having a first end and a second end; i

a second one-quarter wave U-shaped member having a first end and a second end;

an electrically conductive plate;

means for positioning said first and second members parallel but spaced apart from each other, and perpendicular to said plate, said positioning means comprising insulating mounting blocks positioned on said plate, said blocks having two end-receiving sockets therein, each block having the first end of one member and the second end of said other member positioned in the sockets thereof with said ends spaced from said plate;

a first feed wire connected to said first end of said first member;

and a second feed wire connected to said first end of said second member said feed wire connections and the dimensions and spacing of said U shaped mem- 5 6 =bers producing a unidirectional radiation pattern 2,434,893 1/48 Alford et a1. 343-807 normal to said plate. 2,934,761 4/60 lQanQdkoian 34-3708 3,005,982 10/61 Bernfeid 343-742 References Cited by the Examiner UNITED STATES PATENTS 5 HERMAN KARL SAALBACH, Primary Examiner. 2,116,734 5/38 Reinartz 343-741 GEORGE N. WBSTBY, Examiner.

2,167,709 8/39 Cork et a1. 343-85O X 

4. A DOUBLE LOOP ANTENNA COMPRISING: A FIRST ONE-QUARTER WAVE U-SHPED MEMBER HAVING A FIRST END AND A SECOND END; A SECOND ONE-QUARTER WAVE U-SHAPED MEMBER HAVING A FIRST END AND A SECOND END; AN ELECTRICALLY CONDUCTIVE PLATE; MEANS FOR POSITIONING SAID FIRST AND SECOND MEMBERS PARALLEL BUT SPACED APART FROM EACH OTHER, AND PERPENDICULAR TO SAID PLATE, SAID POSITIONING MEANS COMPRISING INSULATING MOUNTING BLOCKS HAVING TWO END-RECEIVING SOCKETS THEREIN, EACH BLOCK HAVING THE FIRST END OF ONE MEMBER AND THE SECOND END OF SAID OTHER MEMBER POSITIONED IN SOCKETS THEREOF; 